Basic concept on virtdev in Django?

Question

Django

I continue to study Django, I was advised that it is better to create my own virtual environment for each project, so in each project I type this
virtualenv --no-site-packages win_venv
win_venv\Scripts\activate
This is on the local machine.
And when I upload it to the hosting, I create a virtual environment separately in the project. And I can't figure out why even this? And is it necessary to re-create the virtual environment here and there separately?

Answer 1

Here you will have two sites on one server. One is old with django 1.6, the other is new with 1.9. And both are in Python3. Understand?

Answer 2

1. Correct the title: virtdev -> virtualenv.
   
2. There is no virtualenv in Django. But you can put Django in virtualenv .
   
3. If you cannot understand why all this is needed, then you probably do not need all this .